1. Field of the Invention
The technical scope of the present invention is that of devices to extract liquids from geological deposits, of the hydrocarbon type.
2. Description of the Related Art
It is known to date how to extract liquids from the ground, for example hydrocarbons, which lie in underground deposits that may be several kilometers deep. After drilling a hole from the surface to the deposit, where the liquid to be extracted lies, the hole is consolidated progressively throughout the drilling process with pipes of tapered diameter. These pipes as a whole constitute a casing. In the production zone, towards the buried end, this casing is pierced with a certain number of holes so as to enable the fluid to accede to the production pipe. This perforated part is termed liner or drain depending on its length. A pipe of constant diameter but smaller than that of the casing is introduced into the preceding casing so as to reach the bottom of the drill hole in order to pump the liquid to the surface. This pipe is thus an extraction pipe.
One problem frequently encountered is that of the low value of the absolute or total flow from the well. This flow is linked to several factors, but it is essentially the viscosity of the liquid being extracted which causes problems. This liquid is all the more viscous in that it is at low temperature. Depending on the composition of the liquids to be extracted, another problem may arise. In the case of a liquid containing fractions able to solidify, for example paraffins or asphaltenes, these fractions tend to solidify and this increasingly as the temperature drops. These fractions tend to precipitate and thus progressively block the orifices in the production zone in the casing and in the oil deposit itself near the casing.
It can thus be observed that the high viscosity and solid precipitations cause said flow to slow down, which increases production costs per volume unit and may cause the closure of a well.
It is known for the injection of heat into an oil well to facilitate the flow from the source rock through the liner or drain. The heat acts in two ways: it reduces the viscosity of the crude oil thereby facilitating its flow and it prevents the formation of precipitations, paraffins and asphaltenes, or even melts those which may have formed before the injection of heat.
To overcome this problem, several solutions have already been applied. Reference may be made to U.S. Pat. Nos. 2,757,738 and 4,344,485.
One solution consists in injecting pressurised water vapor via an extraction pipe. Several drawbacks are incurred. Given the substantial length of a well, which may be of several kilometers, it is difficult to guarantee that the vapor will arrive hot at the bottom of the well. Moreover, the use of the extraction pipe for this requires the total stoppage of production during this phase. This method thus presents the drawbacks of discontinuous production (known as Huff ‘n’ Puff).
The drawbacks to the use of water vapor are well known. Indeed, these devices use great quantities of energy, and need complicated installations for injection and supply which may prove difficult in cold dry countries. Moreover, the injection of water vapor into the reservoir leads to the recovery of an oil/water (condensed steam)/steam residue mixture which then requires a specific installation for the separation of the oil from the water.
Another solution consists in injecting a solvent of heavy fractions into the reservoir zone. One drawback to this is the necessity of providing logistics for this solvent: supply, storage, etc. Another drawback lies in the fact that the chemical action of the solvent only operates on certain fractions. However, the other methods acting by heat injection have a double effect. They act both on the precipitations and on the fluidity of the warmed liquid, thereby improving extractible flow and extraction efficiency.
Another solution by heat injection consists in positioning a heater at the bottom of the well. This heater is advantageously an electrical resistance. The difficulty in diffusing this thermal power causes very high temperatures. Thereafter problems arise from choice of materials, both for the resistance and for the end of the casing and/or the extraction pipe. Given its position at the bottom of the well, it is difficult to make such a resistance both reliable and easily maintainable. Lastly, for safety reasons, it is tricky to introduce great quantities of electrical energy to the well bottom.